k-deformed kinetics underlying water uptake in Nafion (R) 115 membrane

The membrane hydration involves a complex kinetics in which the Nafion®-water system shows variable transport properties for different water state: with the same water activity, the uptake by the membrane is different when it is included in saturated vapor or liquid state (Schroeder paradox). To study the transient humidification process that occurs inside a Nafion® membrane an approach based on different kinetics was proposed.Water uptake has been explained by the superimposition of different diffusion kinetics: a standard and a deformed one according to the Fick's law and the so-called κ-deformed distribution, respectively. For electrodes, gaskets, etc., the linear kinetics underlying the Fick's diffusion behavior has been imposed, whereas the κ-deformed one was introduced to describe the water uptake versus time by the electrolyte membrane only. By means of the global water balance in the whole cell volume, some time evolution parameters useful to evaluate the water uptake have been deduced from the analysis of electric performance. The early experimental results are reported and discussed.